In current dental technique, a carious tooth is restored by drilling out the diseased tooth structure and replacing it with a restorative material. In most cases, this restorative is dental amalgam, a silver mercury alloy. Amalgam is plastic when newly mixed and must be placed into the cavity before it hardens. Unless applied with sufficient pressure, amalgam does not conform to the margins of the cavity satisfactorily. Amalgam also does not bond to the walls of the cavity; instead it is held in place by frictional forces. It is estimated that one half of amalgam restorations fail within ten years and the major reason for this failure is loss of marginal integrity.
An amalgam restoration can fail at the margin for a number of reasons. The amalgam itself can crack and spall away, particularly in restorations where it has been drawn out into a thin layer. Another cause is poor technique on the part of the dentist in not providing proper cavity design, or in not applying the pressure necessary to adapt the amalgam to the margin, or in trying to work with amalgam which had started to harden. Marginal failure can also occur due to thermal cycling during which the tooth structure and the amalgam do not expand at the same rate, thus causing the margin to enlarge.
The result of an enlarged margin, no matter what the cause, is seepage of saliva, oral debris, and cariogenic bacteria into the margin. In some cases a liquid becomes trapped and on warming exerts a painful pressure on the tooth structure and through it to the nerve. The impaction of food into the margin along with cariogenic bacteria produces a situation where the formation of secondary caries is almost inevitable. Thus, it is important to the preservation of amalgam restorations to be able to seal the margins to prevent seepage into them.
In the dental margin, both tooth and amalgam surfaces are of relatively high energy, but the metal surface has considerably higher critical surface tension than those of enamel and dentin. On the other hand, enamel and dentin have a critical surface tension which increases with the increase of relative humidity.
To be effective a sealant must not only manifest good penetration deep into the margins and completely seal the same, but it must manifest very good adhesion to the tooth and amalgam restoration surface. It must shrink as little as possible during cure to prevent loss of adhesion at the tooth/sealant and amalgam/sealant interfaces, and it must exhibit very good cohesive strength and resilience.
Only in this way can the sealant effectively act as a barrier to the entrance into the margin of saliva, food particles, cariogenic bacteria, and other oral debris.
Prior to the present invention, a composition exhibiting all of the above multiple desirable and salutary properties had not been found. The instant discovery provides such compositions.